How can fix this trolling motor?

I have a busted minn kota e-drive on a 2003 escape cruz electric deck boat. This is a 48 volt trolling motor rated a 2hp not sure how many amps it draws. The lower unit is working as I have hooked it up directly to a battery. And the electronic control cable works as I have found continuity on all 11 pins. I want to eliminate the mother board and electronic throttle control and replace it with a rheostat or pot for speed control. I think the mother board might be the problem but there is no way for me to test it as it has that hard black silicone. The only other component I have not tested because of lack of know how is a 4 terminal solenoid that seems to be connected for the key ignition. Please any ideas to get this running again will be appreciated. I am also able to email pics if needed. ThanksHow can fix this trolling motor?
dont know the unit in question but if it's rated 2 hp %26amp; 48 volt it will draw something like 30 amps full power. A rheostat ( or pot) that can handle this sort of current will need to be as big as your head, cost a couple of hundred dollars, get hot %26amp; waste a lot of your battery power as heat.

The solenoid is easy to test. there will be continuity between two of the terminals - apply 12volt ( or it may be 48) across these two %26amp; there should be a click or clunk noise as the contacts pull in giving you continuity across the other two terminals.

Be very careful doing any tests using a car or deep cycle battery as a power source - they can produce very high currents when shorted %26amp; make excellent arc welders for a few seconds, especially at 48 volt.